In some vehicles the side to side loading is intentionally unbalanced, for example, the front left or driver side of a vehicle will be unbalanced when a driver is present. In addition, the driver side has the steering column and mechanism, the instrument panel, and may include other components such as the power steering pump and batteries. The suspension in such vehicles can be designed to accommodate the imbalance by providing stiffer springs, for example. However, this may result in an uncomfortable ride for the driver and passengers. In air suspensions, a side to side imbalance can be accommodated by controlling the air pressure in the air springs.
Height control valves are used to control the height of an air spring by controlling the air pressure, and are used to accommodate imbalance by supplying air to the air springs to maintain both sides of vehicle at a common height. Typically, two height control valves are used, with one on each side of a vehicle to independently control the air pressure in the air springs on each side. However, height control valves are expensive and relatively low reliability items. It is difficult to adjust the height control valves on each side to maintain the same height. In addition, using two height control valves increases the complexity of the suspension system, requiring additional components and air lines.
As a result, illustrated in FIGS. 1 and 2, some air suspension systems utilize a single height control valve 10 to maintain ride height and level of the frame 12. The frame 12 is supported on the axle 14 by air springs 16, 18. Such systems, however, are susceptible to difficulty in side-to-side weight imbalances. Because the height control valve reacts to load conditions for the side of the vehicle on which it is mounted, the opposite side receives the same air pressure. When the load L on each side of the vehicle is the same, as illustrated in FIG. 1, equal air pressure (indicated by gauges 32, 34) in the air springs 16, 18 results in level height of the frame 12. However, because the load on the air springs may be different on the opposite side (and in the case of the designed imbalance, is normally different), the air springs on opposite sides of the vehicle may be set to different heights. This manifests itself, for example, in a leaning chassis that uses this type of air suspension with a single height control valve, as illustrated in FIG. 2, where the load L1 is greater than the load L2, and equal air pressure results in the air spring 16 on the left side of the figure being at a greater height than the air spring 18 on the right side in the figure under the greater load L1.
To correct for the tilting that results from a single height control valve controlling for an unbalanced load, one or more spacers 22 may be added under the air spring 18 on the side with the higher load L1 to accommodate the unequal loading. This is shown in FIG. 3.
While a spacer can correct for a leaning chassis caused by unequal loading and equal air pressure in the air springs, its use has disadvantages. Spacers are difficult to adjust and do not consistently give a predictable result.
To overcome these deficiencies in the art, the invention proposes a new system for maintaining the chassis level in a front air suspension of a truck having a known imbalance.
The system according to the invention utilizes a single height control valve in conjunction with a pressure reduction valve. The pressure reduction valve (PRV) is interposed in the air line feeding the opposite side air springs to reduce the pressure to the air springs on the side of the chassis that has less load. The pressure reduction valve may be permanently preset to account for consistent weight biases. Alternatively, the pressure reduction valve may be adjustable to allow tuning of the vehicle stance.